U.S. Pat. No. 6,827,909 B1 (the entire contents of which is incorporated herein by reference) discloses a catalytic converter for cleaning exhaust gas from a diesel engine including at least one honeycomb body coated with catalytically active material and having passages through which the exhaust gas can flow, walls separating the passages from each other, and first and second zones disposed in succession in a flow direction. The first zone has a lower thermal capacity per unit volume of the honeycomb body than the second zone. In one embodiment the first zone and the second zone are formed by coatings having different thicknesses. The first zone can rapidly reach its operating temperature at high exhaust gas temperatures while the second zone stores heat for operating conditions involving a low exhaust gas temperature.
WO 01/74476 (the entire contents of which is incorporated herein by reference) discloses a multi-zoned NOx absorber comprising a first zone, a second zone and, optionally, one or more intermediate zones disposed between the first and second zone. In the first zone, a catalytic trap material comprises a refractory metal oxide support having dispersed thereon a palladium catalytic component in the amount of about 30 to about 300 g/ft−3, a platinum catalytic component in the amount of 0 to about 100 g/ft−3 and a rhodium catalytic component in the amount of 0 to about 10 g/ft−3; and a NOx sorbent comprising one or more basic oxygenated compounds of one or more alkaline earth metals and optionally, one or more basic oxygenated compounds of one or more alkali metals. In the second zone, the catalytic trap material comprises a refractory metal oxide support having dispersed thereon a palladium catalytic component in the amount of 0 to about 50 g/ft−3, a platinum catalytic component in the amount of about 10 to about 100 g/ft−3 and a rhodium catalytic component in the amount of about 5 to about 20 g/ft−3; and a NOx sorbent comprising one or more basic oxygenated compounds of one or more metals selected from the group consisting of alkali metals and alkaline earth metals. In the optional zone(s), the catalytic trap material comprises a refractory metal oxide support having dispersed thereon a palladium catalytic component in the amount of about 25 to about 75 g/ft−3, a platinum catalytic component in the amount of about 5 to about 30 g/ft−3 and a rhodium catalytic component in the amount of 0 to about 10 g/ft−3; and a NOx sorbent comprising one or more basic oxygenated compounds of one or more metals selected from the group consisting of alkali metals and alkaline earth metals. Therefore, the disclosure suggests that the first zone, followed by an intermediate zone followed finally by the second zone can have a maximum total platinum group metal loading of 410, 115 and 170 gft−3 respectively.
The New European Driving Cycle (NEDC) is used for emission certification of light-duty diesel vehicles in Europe. The NEDC consists of four ECE segments, repeated without interruption, followed by one European Urban Driving Cycle (EUDC) segment. There is no idling period before commencing the first ECE segment. The ECE cycle is an urban driving cycle, also known as UDC, and is designed to represent city driving conditions, e.g. in Paris or Rome. It is characterised by low vehicle speed, low engine load and low exhaust gas temperature. The EUDC segment accounts for more aggressive driving and high speed driving modes. The NEDC is also known as the MVEG-A cycle. The equivalent test cycle to the NEDC in the United States is the FTP-75, which has been supplemented with the US06 segment to reflect aggressive, high speed driving and the SC03 segment, to test for emission standard compliance during operation of air-conditioning. Other countries have adopted their own equivalent test cycles.
Catalysts for oxidising at least carbon monoxide (CO) and hydrocarbons (HC) in exhaust gas emitted from lean-burn engines typically comprise one or more expensive platinum group metal(s) (PGMs), such as platinum, palladium and/or rhodium. A catalyst manufacturer would have a competitive advantage if it could develop a new oxidation catalyst that achieves a better conversion of CO and HC over an entire legislated emission test cycle without increasing the total amount of PGMs, or even using less PGMs, in the new oxidation catalyst relative to a standard oxidation catalyst. For the purposes of this disclosure, a “standard” oxidation catalyst has a uniform washcoat loading and a uniform PGM loading along its entire length.